This invention relates to heat engines, and particularly to a free-piston Stirling cycle engine. Even more particularly, the invention relates to a hermetically sealed posted displacer free-piston Stirling engine driven compressor/alternator.
The conventional spark ignition internal combustion engines which are currently in widespread use in medium power applications, viz, 1-40 horsepower, are unsatisfactory in a number of respects. Although these engines are generally quite reliable and have a good power to weight ratio, the exhaust emissions of these engines contain unacceptable levels of pollutants, the engines are noisy, and the maintenance interval is too short. Most seriously, however, the currently available internal combustion spark ignition engine is so inefficient and dependent on diminishing supplies of increasingly expensive gasoline that the cost of the power it produces is becoming prohibitive.
A free-piston Stirling engine is the logical candidate to replace the internal combustion spark ignition engine in this power range. It is extremely efficient and quiet in operation. Its external combuster can accept virtually any fuel; it requires no oil lubrication, can be hermetically sealed, and requires no maintenance for extended periods of time, measured in years rather than months or weeks.
A difficulty with the free-piston Stirling engine has been in increasing its power output from the low-power applications for which it is been primarily designed, that is in the order of 5-50 watts, to a medium-power application such as a heat pump or alternator in the range of 1-10 kW and higher. The attempts to scale-up the low-power existing free-piston Stirling engines, which essentially have been laboratory curiosities, to the desired power range, reliability, and manufacturability, have been, up until now, fruitless.